1. Field of the Invention
The present invention relates to an electrophoretic apparatus of the type, in which terminal and leading electrolyte chambers are connected to both the terminals of a D.C. high voltage power source circuit, respectively, a migration tube is connected between those electrolyte chambers and a sample injector and a detector are connected in this order in the migration tube.
2. Description of the Prior Art
An isotachophoresis is conducted by charging the inside of a migration tube with two kinds of electrolytes, i.e., terminal and leading electrolytes and by injecting a sample of chargeable substances such as amino acids, peptides or biological substances into the boundary between those two electrolytes to effect the electrophoresis in a constant current so that the substances to be detected may be separated in accordance with differences in their mobilities and may be qualitatively and/or quantitatively analyzed by means of a suitable detector. The isotachophoresis is therefore indispensable for the analysis of a small quantity of sample. More specifically, there is recently proposed in U.S. Pat. Nos. 3,932,264 or 3,941,678 a capillary type isotachophoretic apparatus which uses a capillary tube as a migration tube.
In such cases where the quantity of the sample is remarkably small or where the sample contains two kinds of components having remarkably near mobilities, the analysis cannot be sufficiently conducted by the electrophoretic apparatus according to the prior art. In the former case, more specifically the sample has its obtainable ion component zone so narrowed that it cannot be sufficiently detected. In the latter case, the ion component zones of the two kinds are so close to each other that they cannot be discriminated. If the migration tube is elongated, the analyzability may naturally be improved, which cannot be said to be practical in view of the analyzing efficiency.
On the other hand, in case the sample is brine and has its components in small quantities to be analyzed, the brine itself has many chloride ions which have a large mobility. According to the electrophoretic apparatus of the prior art, therefore, the chloride ion components will be detected for a long time before the target components in the small quantities are detected. This means, in other words, that a useless time period for the analysis is wasted.
In order to solve those problems and to achieve the two objects of shortening the analysis time and ensuring the precise detection, there has been proposed method, in one of which migration current is enlarged at the initial stage of the analysis to enlarge the migration velocity of the ions thereby to shorten the time period required and is reduced at the final stage of the analysis to depress generation of Joule heat thereby to ensure the precise detection. It is important in that method proposed to make proper the timing at which the migration current is to be switched. For this purpose, it is required to detect that the front edge of a predetermined ion component zone of the sample has passed through a predetermined position of a migration tube. As this detecting means, there may be conceived to dispose a detector at the predetermined position of the migration tube separately of the intrinsic detector. In this case, however, since the additional detector has to be disposed in the migration tube, the apparatus is complicated as a whole, and there arises a fear that an interaction between that detector and the sample takes place.